Pickling solution for copper-base alloys



Aug. 13, 1940.

LOGARITHMIC: 2W4 BY 2 3 /4 INCH CYCLES 6 M. I... WOOD FICKLING SOLUTIONFOR COPPER-BASE ALLOYS Filed Aug. 10, 1938 359 no 1149mm m 5901 .LN3383dACI'NAT'NG AGKIIS INNMTEDME 8 NORHM. ll HCTMAJG ION TIME OF IHHERSWN INMINUTES Patented Aug. 13, 1940 UNITED STATES LAUIHHIL'.

PATENT OFFICE PICKLING SOLUTION ALLO FOR COPPER-BASE YS Chase Brass &Copper 00.

Incorporated,

Waterbury, Conn., a corporation Application August 10,

2 Claims.

This invention relates to an improvement in pickling or scale-removingsolutions, and more particularly tmgigkling or scale-removingsolufilonsfor the treatmehtofcoppei base alloys, the surfaces of whichhave become scaled as a result of annealing or other heat treatments.

When sheets, rods, wires, etc., formed of copper-base alloys, areannealed or subjected to other heat treatments, the surfaces of sucharticles become coated with a layer of scale composed mainly of oxidesbut which frequently also includes redeposited metallic films,sulphides, carbonaceous material, etc. Such scale must be removed notonly to improve the appearance of the material, but to render thematerial more workable and render it suitable for welding, tinning,plating, etc. The exact chemical composition of the layer of scale,above referred to, will, of course, vary considerably with thecomposition of the base metal, and also, to a considerable degree, withthe atmosphere surrounding the alloys while they are at an elevatedtemperature. In copper-zinc alloys, either binary or those of a morecomplex character, the zinc has a tendency to diffuse to the surface ofthe alloy when the latter is at elevated temperatures and especiallywhen the zinc is in excess of approximately 20%. The resultant scale iscomposed predominantly of zinc oxide.

In alloys containing from about 10% to about 20% of zinc, the reactionoccurring at elevated temperatures is a very complicated one, and thecomposition of the scale varies considerably with the temperaturemaintained and the character of the surrounding atmosphere. Incopper-zinc alloys containing less than approximately 10% zinc, theresultant scale occurring as a result of annealing or other heattreatments has substantially the same proportions of metals as existedin the base or body material. Furthermore, when small amounts of certainmetals are present in addition to the copper and zinc referred to, such,for instance, as silicon or aluminum, etc., a relatively-largerproportion of these latter metals is usually found to be present in thescale than in the base or body alloy, thus indicating the diffusion ofthese metals to the surface of the article when the same is at anelevated temperature.

In the case of certain of the more complex copper-base alloys, andespecially those containing silicon, great difiiculty is usuallyencountered in completely removing the scale in a manner which willproduce a uniform smooth-textured 1938, Serial No. 224,196

surface, by means of ordinary pickling or scaleremovlng solutions. Asomewhat similar difliculty, though not as extensive, is met inconnection with the pickling of hlgh-nickel-content copper-base alloys,since here the scale is softened and somewhat loosened by ordinary pickling solutions, but is not effectively removed.

By way of example, it may be stated that heretofore when attempting toremove particularly tenacious or recalcitrant scales containing silicon,it has been customary to employ in succession two, three, or even foursolutions in addition to mechanical scrubbing.

In addition to the above, further difiiculties in the treatment ofcopper-base alloys usually result from the particular form, thickness,tenacity and composition of the scale referred to, depending largelyupon conditions of contact between contiguous convolutions or layers ofa coil of wire or rod or of flat bars, strips, or the like, while undertreatment. For instance, where two adjacent layers are annealed inrelatively-tight contact at one point and are relatively well separatedat some other point, a marked difierence in the scale formation at thesetwo positions usually results. Under such conditions, the employment ofordinary pickling or bright dipping solutions usually results in themetal being preferentially attacked at one zone as compared to the otherzone, and the difierences initially apparent in the character of thescale become exaggerated rather than decreased. In particular, it hasbeen found that the difiiculties such as those just referred to are mosttroublesome in connection with the scale appearing upon silicon-bearingcopper-base alloys.

Another difficulty frequently encountered in the pickling of copper-basealloys to remove the scale therefrom is the difficulty due to theredeposition of a film of metallic copper on the base or body metal ofthe article being treated. This redeposition of copper may, forinstance, be due to the presence of a more electropositive metal in thepickling solution, such, for instance, as iron. This redeposited film ofcopper is not readily attacked by the ordinary non-oxidizing picklingsolution, and, therefore, is not removed to a satisfactory degree.Furthermore, the said redeposited film of copper acts as a shield orstopoff which prevents the complete and satisfactory removal of oxide,etc, which may be located beneath the said film, or which may be admixedwith it.

One of the objects of the present invention is to provide a superiorpickling solution for the treatment of copper-base alloys, which willproduce upon such alloys a uniform fine-textured surface substantiallyindependently of variations in the type and amount of scale initiallypresent on such alloys.

Another object of the present invention is to provide a superiorpickling solution for the treatment of copper-base alloys which willguard against the harmful effects of redeposited film of metalliccopper.

A further object of the present invention is to provide, in combinationwith the primary pickling acid or acids, an oxidizing agent which willeffectively oxidize redeposited surface films of copper.

A still further object of the present invention is to provide a superiorpickling solution for the treatment of copper-base alloys which willinclude, in addition to the primary pickling acid or acids, an activatoror accelerator which will act to increase the activity of the primarypickling acid.

Still another object of the present invention is to provide a superiorpickling solution of the character referred to, which will effectivelyperform the scale-removing function of complex scales without requiringthe multiplicity of steps and solutions common in the art for thispurpose.

Another object of the present invention is to provide a superiorpickling solution for the removal of scale from copper-base alloys,which is capable of forming complex ions tending to increase thesolubility of the solution product and, therefore, increase the life ofthe pickling solution.

A further object of the present invention is to provide a picklingsolution of the character referred to, which will effectively removetenacious scale containing such metals as silicon, nickel, etc., by anaction which is both chemical and mechanical in its nature.

A still further object of the present invention is to provide a superiorpickling solution for copper-base alloys which will economically provideupon such alloys a surface of such character as will facilitateresistance-welding of parts made from the said alloys.

With the above and other objects in view, as will appear to thoseskilled in the art from the present disclosure, this invention includesall features in the said disclosure which are novel over the prior art.

The accompanying drawing is a logarithmic curve-sheet or graphillustrating in particular the effects achieved by the addition ofaccelerating or activating agents as compared to pickling solutionswithout such agents,

As will appear more fully from the following, the present inventioncontemplates a pickling solution embodying three main features, namely aprimary pickling acid or a combination of such acids (preferablyinorganic), (b) an oxidizing agent or a combination uf such agents, and(c) an activating or accelera ng agent or a combination of such agents.The designation "activating agent or accelerating agent has been adoptedfor the purpose of clarity of description, since no pretense is heremade that the actual modus operandi of such agents are fully understood,save that their beneficial effects have been clearly determined.

The principal function of the pickling acid constituent of the presentimproved pickling solution is as an agent for effecting the dissolutionand hence the removal of the scale (mainly oxides or the like)originally on the surface of the basemetal and/or the dissolution andhence the re moval of the products of the reaction of the oxidizingagent on the base-metal itself or on metallic constituents (such asredeposited metallic films) of the scale.

One of the principal functions of the oxidizing agent of the presentinvention is to oxidize metals to form compounds capable of beingdissolved by the acid. It might be mentioned that the metals involvedwhen in the metallic state are practically insoluble in simplenon-oxidizing acid solutions.

Another of the principal functions of the oxidizing agent is to maintainthe metallic ion of the activating agent in its state of highest valency(where it has more than one valence), that is, in the state of highestoxidation.

One of the principal functions of the activating or accelerating agentis to increase the activity and therefore the rate of reaction of thepickling acid itself. In certain cases, but not necessarily in all, theactivating agent may also perform the function of an oxidizing agent,but in all such cases its principal function is nevertheless that ofactivating the pickling acid constituent rather than oxidizing metal.

Preferably, the three features of the pickling solution of the presentinvention should embody all of the following characteristics, though itis to be understood that all of the characteristics listed are notessential.

Pickling acids (a) From the standpoint of maximum activity and minimumcost, the acid or combination of acids (sometimes singularly andcollectively referred to herein as pickling acid) preferably should beinorganic, though organic acids may be employed.

(b) The acid or combination of acids should be such that the cupricsalts and the cuprous salts (if formed), and the salts of the othermetals in the alloys, are readily soluble in the solution.

(0) The acid constituent or constituents should have high chemicalactivity.

(d) The acid constituent (whether formed of a single acid or acombination of such acids) should be highly ionized in solutions.

(e) The said acid or acids should preferably, though not necessarily,have a monovalent acid radical.

By way of example, it has been found that hydrochloric acid andsulphuric acid possess to the proper degree the preferred propertiesabove referrred to.

oxidizing agents (a) The oxidizing agent or agents (sometimes singularlyand collectively referred to herein as oxidizing agent) should have ahigh oxidation potential, that is to say, higher than that necessary tooxidize copper to the cuprous or cupric states, or to oxidize cuprousoxide to cupric oxide. The oxidation-reduction potential shouldpreferably be in excess of about 0.51 volt referred to thehydrogen-hydrogen ion couple as zero. When other metals are present inthe scale in any considerable amount, the oxidizing agent or agentsshould have the capacity for similarly oxidizing such other metals.

(b) The oxidizing agent or combination of oxidizing agents should bereadily soluble in the acid component.

(0) The oxidizing agent or agents should be Iii such that all thereaction products thereof will be readily soluble in the picklingsolution.

(11) The oxidizing agent or combinations thereof should be chemicallystable prior to their addition and use. in the pickling solution.

Among the materials suitable for use as oxidizing agents in accordancewith the present invention, the following may be mentioned for purposeof illustration: chlorates or perchlorates of alkali or alkaline earthmetals, peroxides, such, for instance, as hydrogen peroxide andpersulphates, such, for ins ance, as sodium persulphate.

Halogens when used as oxidizing agents may be added in the gaseous formor generated by the passage of an electric current between suitableelectrodes when the solution contains hydrochloric acid or chlorides 0rbromides from other sources.

Similarly, in solutions containing iron or cobalt salts as activators,an electric current can serve as an oxidizing means by reoxidizing theferrous ions to ferric ions and cobaltous ions to cobaltic ions, as someof these higher valence ions are reduced during the dissolution ofmetal. Although the ferric and cobaltic ions are themselves oxidizing,their chief function is nevertheless definitely that of an activatingagent.

It should also be noted that under certain conditions the pickling acidas above described might also perform the function of an oxidizingagent; that is, the acid itself might be oxidizing. Examples of suchwould be nig ic acid or hot strong sulphuric acid.

Activating or Accelerating Agents (a) The activator or accelerator orcombinations of the same (sometimes singularly and collectively hereinreferred to as activating agent) should preferably, though notnecessarily, have the same acid radical as the pickling acid constituentitself.

(b) This agent or combination of agents should preferably, though notnecessarily, have a high valence, i. e., a salt of a bivalent metalwould have a greater activity and, therefore, be preferable to amonovalent salt. For the same reason, a salt of a trivalent metal ispreferable to one of a bivalent metal.

(0) The activating or accelerating agent or should in itself or inthemselves be capable of discharging an oxidizing action on the scaleformation and, therefore, be capable of aiding the direct action of theoxidizing agent or agents as such.

(f) Either neutral or acid salts are suitable activators.

(g) The oxidation-reduction potential, if any, should be less than theoxidation-reduction potential of the oxidizing agent.

By way of example of suitable activating or accelerating agents, thefollowing may be mentioned:

Salts of univalent metals:

Lithium chloride Potassium chloride qll li sammeamate Ammonium chlorideAmmonium sulphate Salts of bivalent metals:

Calcium chloride Magnesium chloride Magnesium sulphate Barium chlorideZinc chloride Strontium chloride Salts of trivalent metals:

Ferric qnaew iq w eeacilrai ing)" Aluminum chloride Aluminum sulphate 35Ferric sulphate (oxidizing as well as activating) Cobaltic sulphate(oxidizing as well as activating) Salts of quadrivalent metals:

Ceric sulphate (oxidizing, as well as activat- The constituents hereinreferred to may be combined in almost innumerable ways and prorportions. Generally speaking, the pickling acid (or combinations of thesame, also included in the term pickling acid) may fall within the rangefrom about 2% to more than 20% by volume; the oxidizing agent (orcombinations of r agents should have a high degree of solubility thesame, also included in t t pickling in t pickling solutwn used Incombmatwn acid) from about 0.1% to about 25% by weight; therewith. andthe activating agent (connoting also com- (d) The reaction products ofthe actlv or binations of the same) from about 0.25% to about 4 oraccelerators should have a high degree of 20%. n solubility in thesolution. The following examples of complete pickling (e) Preferably,but not necessarily, the activatsolutions embodying the presentinvention, are ing or accelerating agent or agents employed illustrativeonly and not restrictive:

Acid

- oxidizing agent Activator No. (commercial purity by volume in water)(by weight) (by Wel=ht) 3% hydrochloric. 0.1% sodium chlorate 3% ferricchloride.

3% hydrochloric 0.5% sodium chlorate. 10% ammonium chloride. 10%hydrochlor c. 0.25% sodium chlorate l 5% ferric chloride. 10%hydrochlor1c 0.15% calcium chlorate 7% ferric chloride. 5

7% hydrochloric 0.35% ammonium persulphat 8% ferric chloride and 4%magnesium sulphate. 6% sulphuric 0.15% potassium chlorate 9% ammoniumsulphate. 15% sulphuric 0.2% hydrogen peroxide... 6% fcrrlc sulphate and6% aluminum chloride. 20% sulphuric 0.35% sodium chlorate 7% ferricchloride and 10% sodium chloride. 10% sulphuric 0.2% ammoniumpersulphate 10% ferric sulphate and 5% ferric chloride.

5% hydrochlor 0 25% hydrogen peroxide 4% ammonium chloride and 6%calcium chloride. 8% hydrochloric. 0 4% calcium chlorate. 10% ferricchloride and 5% aluminum chloride. l2 213277 lfiygrocmor c. 0.25 sodiumhypochlorite 8% ferric sulphate and 6% ammonium sulphate. l0 13 y meChlorine (added in gaseous state to 77 ferric chloride. {4% Sulphunccontinuously form appreciable u 2 amounts of hypochlorus acid). 14 10%hydrochlor1c 0.1% sodium chlorate and 0.35% 10% ferric sulphate and 5%ferric chloride.

ammonium persulphate.

ill)

When ferric salts are used as activating agents, such salts also act inpart as oxidizing agents and may be repeatedly added as such to thepickling solution when necessary, or such salts may be continuouslyregenerated either by electrolytic oxidation or by the addition of otheroxidizing agents as, for instance, sodium chlorate, in which lattercase, the ferric salt would really act as an oxygen carrier. In'eithersuch event, the cost of maintaining such oxidizing agent may bematerially less than were the ferric salt alone to be relied upon as anoxidizing agent.

By way of example, let it be considered that the copper-base alloy beingpickled is one containing approximately 77% copper, 22% zinc and 1%silicon.

Under these conditions, when the improved pickling solution of thepresent invention is employed for the removal of scale from such analloy as that above referred to, the scale will include under ordinaryconditions cuprous oxide, cupric oxide, zinc oxide, and silicon dioxide.

As the scale removing takes place, the oxidizing agent acts to convertcertain of the cuprous oxide to the cupric oxide state and further actsupon the base metal itself to a measurable degree to convert the sameinto oxide forms. The primary pickling acid is thus enabled to morereadily dissolve the scale when the same is oxidized to the cupric stageand also to dissolve portions of the surface of the base metal itself tominimize pittings, scale marks, etc., when such base metal is, asdescribed, oxidized by the oxidizing agent or agents. The zinc oxidepresent in the scale will be quite readily soluble in the primarypickling acid and the zinc of the base metal will be oxidized by theoxidizing agent so as to become readily soluble in the primary picklingacid.

In such cases as a redeposition of copper should occur upon the scale,such redeposited copper will be oxidized and dissolved in the solution.

By the actions above described, the remaining silicon dioxide decomes soloosened as to be readily removable by agitating the copper-basearticles in the bath, or by mechanical scrubbing where necessary, but inany event, the normallytenacious film of silicon dioxide is renderedquite tractable.

With respect to the action of the activating agent or agents, nopretense is here made that the actual modus operandi of such agent oragents is fully understood, save that their beneficial effects have beenclearly determined. It

may here be acknowledged that according to some accepted chemicaltheories, the addition of the activating agent or agents to the solutioncontaining the primary pickling acid or acids and the oxidizing agent oragents should deleteriously affect the result, but contrary to suchchemical theories, the effect actually is directly the reverse, as maybe readily seen by reference to the accompanying drawing, which clearlyindicates the beneficial effects of the activating agents.

The graph shown in the accompanying drawing indicates the relative rateat which the metal of the copper-base alloy is taken into solution and,hence, is similarly indicative of the efliciency of pickling solutionsof the present invention in cleaning scale, etc., from copper-basealloys.

The graph or curve sheet further shows quantitatively the effect ofadded salts or activators on the rate of attack on a silicon brass (77%Cu 22% Zn1% Si) in an acid solution with an oxidizing agent. Theindividual solutions have the same equivalent or reacting weights of thevarious salts used. It should be noted that salts of mono-, biandtrivalent metals are used, and that they range from those of thealkaline metals (sodium and potassium) through the alkaline earths(magnesium and calcium) to the heavy metals (iron and aluminum).

The following general conclusions may be drawn from a study of thecurves shown in the diagram:

(0.) The chloride of any metal whether it be alkali, alkaline earth orheavy metal, is invariably more effective when used as an activator inhydrochloric acid solution than is the sulphate of the same metal. Thiseffect is illustrated by the relative position of curve 5 and thepositions of curves I and 2; by the position of curve 8 and that ofcurve 4; and by the position of curve l0 and that of curve 9.

(b) The higher the valence of the metallic ion used for a given negativeion, the greater the effect (with the exception of aluminum chloride).This effect is illustrated by the successively higher positions occupiedby curve 5, curves 6 and 8, and curve In. The relative positions ofcurve I and curve 8 illustrate a slight exception to this generalconclusion.

(c) All of the added activating agents used, markedly accelerate theaction of the base solution except the sulphates of potassium andsodium. As explained in more detail below, the apparently anomalousbehavior of these salts may possibly be due to differences in hydrationof the silica. This effect is illustrated by the relatively-higherpositions occupied by curves 4 to ID inclusive as compared to theposition of curve 3 and the exception to this general rule isillustrated by the relatively-lower positions of curves I and 2 comparedto that of curve 3.

The tests represented in the accompanying drawing were made on identicalspecimens suspended in the various solutions indicated. The compositionof the base-metal was substantially 77% copper, 1% silicon, remainderzinc. By a cam arrangement, the specimens were alternately raised andlowered to give the same amount of stirring to all the specimens. Exactcontrol of stirring is important in such tests on siliconcopper alloysbecause of the largely mechanical removal of the siliceous film. Loss ofweight of the specimens was selected as the basis of comparison.

By way of example, a generally used commercial practice requires twentyminutes for the removal of the black scale which is largely cupricoxide. With some of the activated solutions of the present invention,the same result is obtained in one to two minutes and the whole picklingprocess takes only about eight minutes. After the removal of the blackscale, the process is largely the formation of a gelatinous film withthe silica in the scale and slight dissolution of the basemetal. By thecombined action of mechanical agitation and slight dissolution of thebase-metal, the gelatinous film of hydrated silica is removed.

In these solutions of the same equivalent concentrations, salts withhigher valence are more effective. Additions of sulphates to HClsolutions are not as effective as the same concentration of the samepositive ion added as a chloride. This point is very important in itsrelationship to the common ion effect which, according to classicalphysical chemistry, might be expected to give exactly the oppositeresult.

The fact that so many salts of widely difiering character give anincreased rate of dissolution shows that the general principle of addinga salt as an activator is experimentally demonstrated. In fact, thissame efl'ect has been amply demonstrated by large-scale commercialpractice wherein marked improvements in the quality, lowering ofpickling time and cost in the treatment of copper-base alloys have beenattained by the use of pickling solutions of the present invention. Notonly has a marked improvement in the appearance and uniformity of thesurface of the metal resulted, but the cost of the operation has beenfound to be but a fraction of the cost incident to the use of the bestpickling solutions of the prior art.

The eil'ect of variations of valence of the activating agents is ingeneral clearly shown. The fact that aluminum chloride is somewhat lesseffective than magnesium chloride may be due to diflerences in hydrationof the silica or some specific eflect of the ion; but the solution rateis greater than for calcium, sodium or potassium chlorides. :iu alts aremore energetiein e Ierricioiis an oxidizing agen as well as an ac mtor.The lower rate of dissolution efiected'b'y solutions containingsulphates as activating agents, as compared to solutions containingchlorides as activating agents, may also be due to differences inhydration of the silica. This may be inferred from the appearance or thegelatinous film developed during the pickling treatment, whichappearance has been found to vary in different solutions.

The invention may be carried out in other specific ways than thoseherein set forth without departing from the spirit and essentialcharacteristics of the invention, and the present embodiments are,therefore, ot be considered in all respects as illustrative and notrestrictive, and all changes coming within the meaning and equivalencyrange of the appended claims are intended to be embraced therein.

I claim:

1. The method of removing scale from copperbase alloys comprisingsubjecting a copper-base alloy to the simultaneous action in water of: apickling acid dominantly of hydrochloric acid; an oxidizing agent havingthe power to oxidize copper to the cuprous state and selected from thegroup consisting of chlorates, persulphates, peroxides andhypochlorites; and an activating agentselected from the group consistingof chlorides of the metals calcium, iron, magnesium and aluminum.

2. The method of removing scale from copperbase alloys comprisingsubjecting a copper-base alloy to the simultaneous action in water of:approximately 0.5% to 12% by weight of hydrochloric acid; an oxidizingagent comprising a substantial amount of sodium-chlorate not materiallyin excess of about 1% by weight; and an activating agent comprisingapproximately 0.25% to 20% by weight of ferric-chloride.

MAURICE L. WOOD.

